Some projectors connect with a terminal over Ethernet (registered trademark) or by wireless communication instead of connecting with the terminal via a VGA cable. Some of these projectors allow a connected terminal to download image data being projected upon request. A conventional projector with a wireless communication function will be described below using FIG. 12. FIG. 12 depicts a parallel control relationships between a projector 1 and four terminals (terminals A to D). Note that the leftmost column shows the contents of an image being projected at that time by the projector for the purpose of the explanations.
When the projector is first activated, an application therein starts to project a setting menu onto a projector screen (step S1). A user sets the wireless connection parameters such as the SSID (Service Set ID) and establishes a wireless basic service set (IBSS: Independent Basic Service Set or BSS) (step S2). Note that the projector and each terminal are connected in ad hoc mode or infrastructure mode.
In the meantime, a user starts an application on the terminal A (step S3). The user of the terminal A designates the same SSID as the one of the projector and makes a connection request to the projector (step S4). In return, the projector sends a response which allows a connection (step S5). Upon this, screen data is sent out from the terminal A, and the screen data of the terminal A is projected onto the projector screen through the projector (step S6).
The terminal B follows the terminal A and performs the connection operations in the same manner. At this time, to control the projector, the following operations can be performed:    (1) the operation of switching to a mode of displaying only the screen data of the terminal B;    (2) the operation of switching to a multimode for simultaneously displaying the screen datas of the terminals A and B; and    (3) the operation of not allowing the terminal B to use the projector and continuously displaying the screen data of the terminal A.
Assume here that the projector is set to the multimode of simultaneously performing display of the terminals A and B. In response to a connection request from the terminal B (step S7), the projector 1 sends in return a response of permission (step S8). Since the projector 1 is set to the multimode, transmission of the screen data of the terminal A continues (step S9). The screen data of the terminal A is combined with that of the terminal B (step S10) to form and project one screen (multi-screen). As a method of forming a multi-screen at this time, the following methods are available:                a method of sending data of the entire screens from the terminals A and B, performing image processing in the projector, and forming a multi-screen; and        a method of sending, via the terminals A and B, images with lower resolution for multi-screen display and combining the images at the projector to form a multi-screen.        
Some of such projectors can temporarily store displayed screen data in their memories or download stored image data to a terminal. For example, if user a of the terminal A performs a screen holding operation using a remote control, the projector detects the operation and accumulates the image being displayed in a holding memory (step S11). After that, when the terminal A requests a download (step S51), data transfer starts (step S52).
In the above-described case, downloading stored image data is unlimitedly performed. More specifically, delivery destinations cannot be limited to specific terminals. Apart from this, there is also demand to set, for each terminal, whether download is permitted (e.g., the terminal B can download an image provided by the terminal A, but the terminal C is prohibited). In this case, one could consider as an arrangement in which if the terminal B requests downloading a screen data displayed by the terminal A, it is checked whether or not the terminal A gives permission to download the data to the terminal B. This arrangement requires the user of the terminal A to recognize that the request comes from the terminal B which has requested download.
Japanese Patent Laid-Open No. 2003-085112 describes means, in a system using a projector, by which the user of a terminal recognizes another terminal serving as a partner. Japanese Patent Laid-Open No. 2003-085112 describes, as the system using a projector, an arrangement which performs exclusive or cooperative remote control for a conferencing system using a plurality of terminals, automatic draw-up of the minutes, synchronization of video, audio, and still images, mirroring with a remote device, participation right control, and the like. According to Japanese Patent Laid-Open No. 2003-085112, pieces of pre-registered user information (photographs of faces, icons, and the like) are used as means by which the user of each terminal recognize a partner.
Japanese Patent Laid-Open No. 2002-281468 describes an arrangement which calculates the positional relationship among pieces of information equipment on the basis of the reception delay time of radio waves and visually shows the placement of the pieces of information equipment on a part of a common screen on the basis of the calculated positional relationship. According to Japanese Patent Laid-Open No. 2002-281468, an information terminal brought in by a participant is arranged as an icon on a virtual screen imitating an actual positional relationship, and a selected file is dragged and dropped onto the icon indicating the information terminal, thereby performing file transfer.
In the conventional examples, screen storage is performed by a storage operation of the projector (step S11), thereby allowing each terminal to download a screen data. This may bring about a situation where data is stored or delivered to an unspecified terminal regardless of the intention of the owner of the data.
In order to determine for each terminal whether to permit download as described above, a terminal serving as the provision source of an image needs to specify each terminal. Examples of a method of specifying a terminal include a method of registering in advance user information to the terminal and associating terminals with their users, as described in Japanese Patent Laid-Open No. 2003-085112. However, this method requires previous settings, and the operation is troublesome. Also, the method lacks flexibility and, for example, cannot cope very easily with a case where there is a change in participants in a conference. As means for specifying a terminal without such previous settings, there exists available a technique for specifying the position of a terminal using communication delay time, as described in Japanese Patent Laid-Open No. 2002-281468. However, if participants are close to each other, an error is likely to occur, and the technique lacks accuracy. Although there is another method of associating terminals with users by taking photographs of the faces of the users or the like with a camera provided and displaying the association, it costs a lot to equip all users with cameras.